Urea-modified ammonium nitrate-fuel oil explosives

ABSTRACT

An ANFO explosive which is modified by the presence of small amounts of urea so that the explosive will not adversely react with pyrite in pyrite-bearing mines.

United States Patent [191 Mason et al. [4 1 Jan. 2, 1973 [54] UREA-MODIFIED AMMONIUM References Cited NITRATE-FUEL OIL EXPLOSIVES UNITED STATES PATENTS [75] Inventors: Charles M. Mason' David R.

. y, both of Bethe] Park, Pa. 3,116,185 12/1963 WllSOl'l et a1 ..l49/46 X 3,190,777 6/1965 Breza et al ..l49/46 X [73] Assignee: The United States of America as 3,447,982 6/1969 Minnick ..149/46 represented by the Secretary of the 3,450,582 6/1969 Sheeran et a1. ..149/46 X Interior [22] Filed: Dec. 10 1970 Primary Examiner-Stephen J. Lechert, Jr. [211 App] No 97 026 Attorney-Ernest S. Cohen and M. Howard Silverstein V W H i, 9 i 1 BST C V i it (C11 An ANFO explosive which is modified by the [581 Fieldoiehreli. j. :j 149/46 2 mums that the sive will not adversely react with pyrite in pyrite-bearing mines.

1 Claim, No Drawings UREA-MODIFIED AMMONIUM Nl'lRATE-FUEL OIL EXPLOSIVES This invention relates to prilled ammonium nitratefuel oil (ANFO) explosives.

Such-explosives generally consist of the combination of prilled ammonium nitrate with about 5-10 percent of its weight of a liquid hydrocarbon such as fuel oil, kerosene, and the like. It has attained widespread use as a blasting agent in hard rock and metal mines. However, it cannot be safely employed in mines with relatively high temperature where significant pyritic minerals are present, e.g., copper-bearing ore bodies, because pyrite tends to react with the ANFO explosive, and causes fumes, fires or even initiates premature detonation. Bureau of Mines Report of Investigations No. 7187 discloses these problems.

We have now discovered a modified ANFO explosive which, can safely be employed in the presence of pyrite and pyrite-bearing ores and minerals at much greater temperatures than heretofore. Generally, our invention comprises incorporating small quantities of urea in the ANFO explosive. This is not to be confused with the invention described in US. Pat. No. 3,447,982 wherein urea is added to ammonium nitrate if the ammonium nitrate is not porous enough to absorb at least 5 percent of its own weight of the oxidizable substance, e.g., liquid hydrocarbon. Our invention relates to the use of conventionally produced, sufficiently porous ammonium nitrate prills, e.g., wherein the prills are obtained by spraying a concentrate of solution into a prilling tower, and wherein the prills can absorb at least 5 percent of their own weight of the oxidizable substance.

It is therefore an object of the present invention to provide an ANFO explosive that does not adversely react with pyrite when dry or in contact with water or acid mine water.

Another object is to provide such an explosive that can be safely employed in the blasting of mines containing pyritic minerals.

Other objects and advantages will be obvious from the following more detailed description.

In the practice of the present invention, particulate urea, usually in powder. form, is added to the prilled AN prior to the addition of fuel oil, or conversely may be added to the AN liquor prior to the prilling operation. Generally, it is incorporated in an amount of about 0.25 to 2.0 weight percent of the explosive composition, preferably in an amount of about 0.5 to 1.0 weight percent.

Thereafter, the ANFO manufactured from the ureatreated prills can be handled, loaded, and fired in identical fashion to untreated ANFO.

The following examples illustrate the effectiveness of the present invention.

EXAMPLE 1 Several 350 gram-samples were prepared of explosive compositions in admixture with wt. pct. pyritic ore, and subjected to simulated borehole tests to determine the temperature of incipient decomposition of the compositions. Some of the samples included water or acid solution which liquids often are present in boreholes. The results were as follows:

TABLE 1 AN-i-ore AN+6wtpctFO+ore Dry 5pct Spct Dry 5pct Spct H,O acid H,O acid Temperature (F) of incipient decomposition A. No urea present 185 185 240 205 150 B. 0.5 wt pct urea 350 360 355 400 250 250 l 0.34 wt pct H,SO solution EXAMPLE 2 A differential thermal analysis (DTA) was carried out in laboratory test tubes to closely observe the effects of urea addition. Several 5-gram samples were prepared of explosive compositions in admixture with 10 percent by weight of pyritic ore. Water or acid solution was included in some of the samples, and the E-sample ebullition with exotherm B-sample ebuliition without pronounced exotherm N-no reaction; sample melted at 340 F 1/ 0.34 wt pct H2804 solution As can be seen from these examples, the reaction between pyrite and ANFO is prevented, by the addition of urea, at temperatures up to the melting point of the ammonium nitrate. The use of ANFO prepared from AN-containing urea results in a decided improvement in the art of using ANFO to the extent that it is feasible to use ANFO in, for example pyritic-copper-orebodies where it has not hitherto been possible due to the high temperature present in the orebodies.

What is claimed is:

1. In an explosive consisting of prilled ammonium nitrate-fuel oil (ANFO), wherein said ammonium nitrate alone is porous enough to absorb at least 5 percent of its own weight of said fuel, the improvement of incorporating urea in said explosive in an amount of about 0.5 to 1.0 weight percent so as to elevate the temperature of incipient decomposition of said explosive when in contact with pyrite. 

